The present invention relates to a one-way clutch. The one-way clutch is used for a pulley of auxiliary machinery such as a feed mechanism for various equipment, an alternator for an automobile, and a compressor, a water pump, and a cooling fan for an air conditioner, for example.
Some one-way clutches are of a type disposed between an outer ring and an inner ring which are disposed inside and outside each other in a diameter direction and concentrically with each other. The clutch functions by switching between a lock state in which the outer ring and the inner ring are rotated synchronously with each other and a free state in which the outer ring and the inner ring are rotated with respect to each other.
Such one-way clutches include a type of clutch employing rollers for the above clutch function. The rollers of this type of one-way clutch are disposed in wedge-shaped spaces formed at some positions on a circumference of a space in a diameter direction and through which the inner and outer rings face each other. A gap in each of the wedge-shaped spaces in the diameter direction narrows in one direction in a circumferential direction. Through the wedge-shaped spaces, cam faces of the outer ring and an outer peripheral face of the inner ring face each other. The cam faces have recessed curved faces which are recessed outwardly in the diameter direction. The cam faces are provided at some positions on a circumference of an inner peripheral face of the outer ring and the outer peripheral face of the inner ring being disposed on an inner side of the outer ring in the diameter direction.
In the above one-way clutch, the lock state is obtained by rolling the rollers to narrower sides of the wedge-shaped spaces to engage the rollers with the cam faces of the outer ring and the outer peripheral face of the inner ring. The cam faces are operating faces for the rollers and to integrate the outer ring with the inner ring. In this case, the engagement can be achieved by friction forces of the rollers against the operating faces.
In such a one-way clutch, a lubricant is used to lubricate the rollers and the operating faces thereof in order to improve abrasion resistance. In this case, although the lubricant is effective at improving the abrasion resistance, an engaging property is reduced and the switching operation of the one-way clutch becomes unstable if the lubrication works excessively in the lock state.
By using urea-based grease which is conventional as a lubricant, both the abrasion resistance and engaging property can be obtained in a relatively narrow range of temperature, but it is hard to obtain both in a wide range of temperature from a low temperature to a high temperature. Specifically, the engaging property of the rollers is poor at the low temperature while the abrasion resistance is poor at the high temperature.
According to the present invention, a one-way clutch is mounted to an alternator and allows rotation of a rotor of the alternator to continue by an inertial force of the rotor when a rotation speed of the crankshaft decreases, thereby improving power generation efficiency. According to such a structure, the abrasion resistance is likely to decrease because vibration of an engine is transmitted almost all of the time to a pulley of the alternator through a belt for rotating the pulley.
Therefore, it is a main object of the present invention to provide a one-way clutch in which an operation of switching between lock and free states in a wide range of temperature from a low temperature to a high temperature is stable.
It is another object of the invention to provide a one-way clutch in which both an engaging property and abrasion resistance are obtained in the wide range of temperature.
It is yet another object of the invention to provide a one-way clutch in which movement of rollers is stable even at a low temperature and the abrasion resistance of the rollers and operating faces of the rollers is improved even at a high temperature.
Other objects, features, and advantages of the invention will become apparent from the descriptions below.
According to the invention, a one-way clutch includes an outer ring, an inner ring disposed inside the outer ring in a diameter direction and concentrically with the outer ring. The one-way clutch also has a state switching component for switching between a lock state in which the outer ring and the inner ring are rotated synchronously with each other and a free state in which the outer ring and the inner ring are rotated with respect to each other. The one-way clutch further includes a lubricant for lubricating an operating portion of the state switching component, wherein the lubricant is prepared by mixing a urea-based consistency increasing agent into ester-based or synthetic oil-based base oil with a pressure viscosity coefficient (at a temperature of 25xc2x0 C.) set at 12 GPaxe2x88x921 or more.
In the invention, because of the selection of ingredients used in the lubricant, movement of the state switching component is stabilized even at low temperature and the state switching component and the operating faces are less likely to wear even at high temperature.
Preferably, the state switching component is a roller disposed for rolling in a wedge-shaped space formed between an inner peripheral face of the outer ring and an outer peripheral face of the inner ring. In this case, the roller is less likely to slip when rolling against a narrower side of the wedge-shaped space.
Preferably, a ratio of the base oil and the consistency increasing agent mixed to prepare the lubricant is set such that the lubricant has a consistency in a range of 240 to 310 (at a temperature of 25xc2x0 C.) and a traction coefficient of 0.02 or more (at a temperature of 25xc2x0 C.). As a result, the movement of the state switching component, for example, the roller is further stabilized.